Trigger the activation hook outside the text editor.

src/workspace.coffee

@@ -550,9 +550,15 @@ class Workspace extends Model
     @project.bufferForPath(filePath, options).then (buffer) =>
       editor = @buildTextEditor(_.extend({buffer, largeFileMode}, options))
       disposable = atom.textEditors.add(editor)
-      editor.onDidDestroy -> disposable.dispose()
+      grammarSubscription = editor.onDidUseGrammar(@handleDidUseGrammar.bind(this))
+      editor.onDidDestroy ->
+        grammarSubscription.dispose()
+        disposable.dispose()
       editor
 
+  handleDidUseGrammar: (grammar) ->
+    @packageManager.triggerActivationHook("#{grammar.packageName}:grammar-used")
+
   # Public: Returns a {Boolean} that is `true` if `object` is a `TextEditor`.
   #
   # * `object` An {Object} you want to perform the check against.